1. Field of the Invention
The present invention relates to the weighing of items by employing a four (4) load cell configuration that permits for the optimum cancellation of all ambient environmental vibration in both the horizontal and vertical planes. The four load cell configuration is implemented in an apparatus where a tare weighing and a gross weighing are always performed for each and every item presented for weighing so to avoid all adverse temperature effects. The apparatus is used for both “static” and “dynamic” weighing. In a static configuration, the item is placed and removed from the weighing assembly using robotics, etc., while for a dynamic configuration the items are conveyed across the weighing assembly using some sort of conveyance mechanism. For static weighing, a minimum weighing rate of one (1) tare and gross weight reading per presentation per second is provided. For dynamic weighing, a rate of weighing of up to ten (10) tare and gross weight readings per second of twenty (20) weight readings per second in total are provided.
2. Description of the Prior Art
Heretofore, various mechanical and electrical systems have been proposed for correcting for environmental vibrations in weighing systems. Examples of analogous and non-analogous systems are disclosed in the following analogous and non-analogous U.S. Patents.
U.S. Pat. No.Patentee3,446,299Lenowicz3,731,754Godwin, et al.4,102,421Ozaki, et al.4,212,361Stocker4,593,778Konishi, et al.4,926,359Konishi, et al.5,117,929Nakamura, et al.6,013,879Nakamura, et al.U.S. Pat. No. 3,446,299 to Lenowicz, U.S. Pat. No. 3,731,754 to Godwin, U.S. Pat. No. 4,102,421 to Oazki, U.S. Pat. No. 4,926,359 to Konishi, U.S. Pat. No. 5,117,929 to Nakamura and U.S. Pat. No. 6,013,879 to Nakamura all teach some form of Analog to Digital conversion in a weighing apparatus. They all take one or more analog weight readings and perform an instantaneous conversion at a fixed point in time. The point in time selected might just happen to be a point in time when significant vibration is being experienced, thus resulting in inferior data.
U.S. Pat. No. 3,446,299 to Lenowicz teaches a data clocking method somewhat similar to the data clocking method disclosed herein.
U.S. Pat. No. 3,731,754 to Godwin teaches a count that is output as a pulse train of fixed frequency.
As will be described in greater detail hereinafter, in the apparatus of the present invention a voltage-to-frequency (V/F) conversion is performed. Such voltage-to-frequency conversion functions substantially different from an analog-to-digital (A/D) conversion. Instead of purely converting an analog signal to a digital signal at a specified fixed point in time, the operation of a voltage-to-frequency converter is such that a continuous pulse train is always present. The frequency, or time period of the pulse, observed coming out of the V/F converter at a given point in time is the instantaneous reflection of the analog voltage at the input to the V/F converter at that very same given point in time. The represented output frequency is always linearly proportional to the input analog voltage level. Therefore, it becomes obvious, that as the input analog voltage fluctuates, the output frequency pulse train will fluctuate as well, in a linear manner. It follows that if a pulse train containing fluctuations in frequencies is accumulated over a fixed time interval, the final count represents an average of the analog voltage applied during that entire fixed time interval. Employed in this fashion, a V/F conversion over a fixed time interval, is an electronic natural means of averaging out noise present on an analog signal, be it Johnson Noise, or other random noise components, so long as they are significantly shorter in period than is the fixed time sampling interval.
Many benefits result from transmitting such a continuously varying digital pulse train. Being digital in nature the pulse train is not susceptible to undesirable electrical noise interference found in hostile environments like in a factory. Moreover, the data can be transmitted over great distances using coaxial cable, fiber-optics, etc. Then, at the receiving end, the data pulses need only to be accumulated over the desired fixed time interval in a counter. Therefore, unlike an A/D converter where numerous conversions may have to be performed and then averaged by the computing device, with V/F conversion, once the fixed time accumulation of pulses has expired, the computing device need merely read the counter.
U.S. Pat. No. 4,212,361 to Stocker, U.S. Pat. No. 4,593,778 to Kornishi, U.S. Pat. No. 4,926,359 to Kornishi, U.S. Pat. No. 5,117,929 to Nakamura and U.S. Pat. No. 6,013,879 to Nakamura all teach the use of a second or dummy load cell in a weighing apparatus.
U.S. Pat. No. 6,013,879 to Nakamura's shows sloping load output lines resulting from the use of two load cells. However this patent does not teach applying a load traversing rigid member connecting the two active cells or connecting two passive load cells. The rigid member serves two purposes. The main purpose is for the reduction of all horizontal vibration components based on the 180 degree out of phase mounting of the two respective load cells connected by the rigid member. The second purpose is for attaching a weighing surface to it, across which is conveyed a dynamic weighing. It is an expectation that the resulting sloping load cell output signals, the slope opposite for each respective load cell, are the result of the load being conveyed across the weighing surface, by physically starting immediately above one load cell and ending up immediately above the other load cell. In between are varying degrees of load exerted on the load cells when an object is somewhere in-between them.
As will be described in greater detail hereinafter in the weighing apparatus of the present invention, four load cells are employed. Each set of two load cells (serving as one assembly) are used to cancel-out horizontal vibration noise components. The additional set of two load cell assemblies further provide a mechanism for canceling-out vertical vibration noise components.